liquid crystal display device with an anisotropically reflecting layer and  manufacturing method for the same

ABSTRACT

A liquid crystal display device comprises an optically diffusively reflecting layer arranged to maximize utilization of incident light. The reflecting layer contains a thin metallic film with projections ( 14   a ) each having an unsymmetrical cross section to centralise reflected light in a specific azimuth direction (y). The range of viewing angles (θ x-z , θ y-z ) into which a substantial portion of the incident light is reflected is broader in the specific azimuth direction (y) than in another direction (x). The director ( 5   d ) of liquid crystal molecules initiallly lies in a plane (y-z) parallel to the specific azimuth direction (y) to achieve retardation self-compensation.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a reflective or transflective liquidcrystal display device and its manufacturing method. The inventionespecially relates to a liquid crystal display device having a diffusivereflecting layer providing distribution of diffused reflected light witha specific directivity.

2. Description of the Related Art

Prior to now, there has been a reflective liquid crystal display deviceprovided with a liquid crystal layer for performing optical modulationin accordance with an image to be displayed and a diffusive reflectinglayer disposed on the back side opposite to the display face isconventionally available. Such a display device causes light, which hasbeen incident from the front side of the display device and has passedthrough the liquid crystal layer, to be diffusively reflected by thediffusive reflecting layer and returned to the display face side throughthe liquid crystal layer again, whereby image displaying is performedusing the light modulated by the liquid crystal layer.

The diffusive reflecting layer used here is intended to prevent theexternal light incident from the display face side of the display devicefrom regularly reflecting and mirror-reflecting the image on theexternal light side and allow the displayed image to be fully visuallyrecognized even if the user changes a viewing angle to some extent.

As a reflective liquid crystal display device used for a portableinformation terminal or the like, there is known a kid of devicearranged to intentionally differentiate a diffused reflected lightdistribution in the case where the screen is viewed from the front atdifferent angles in the vertical direction from a diffused reflectedlight distribution in the case where the screen is viewed from the frontat different angles in the horizontal direction in an attempt to makeefficient use of light adapted to the mode of use in the portableinformation terminal or the like (see Patent Document 1, for instance).

[Patent Document 1]

Japanese Patent Application Laid-Open No. 177106/98 (paragraph number0128 of the 11th page to paragraph number 0130 of the 12th page, FIGS.27, 28, 51 and 52)

However, such a liquid crystal display device with a diffused reflectedlight distribution having a predetermined directivity is not intended toimprove a quality of displaying by maximizing the utilization of thedirectivity in addition to effective use of light, which is achieved byadaptation for the above-described mode of use.

SUMMARY OF THE INVENTION

The present invention has been implemented in view of theabove-described problem and its object is to provide a liquid crystaldisplay device which maximizes the utilization of the directivity of thediffused reflected light distribution of the diffusive reflecting layerand can further improve a quality of displaying.

It is another object of the present invention to achieve efficientimprovement of contrast characteristics, which is suitable to a liquidcrystal display device comprising a diffusive reflecting layer havingdiffused reflected light distribution with a directivity.

In order to achieve these objects, an aspect of the present invention isa liquid crystal display device comprising a liquid crystal layer forperforming optical modulation in accordance with an image to bedisplayed and a diffusive reflecting layer for diffusively reflectinglight having passed through the liquid crystal layer to the liquidcrystal layer with a diffused reflected light distribution having apredetermined directivity, wherein—the diffusive reflecting layer has afunction of giving the reflected light a diffused reflected lightdistribution in which: a first range of viewing angles within whichreflected light rays of luminous flux of predetermined proportion of thefirst total luminous flux of reflection are obtained is defined, thefirst total luminous flux being obtained in a specific plane includingan imaginary axis of a specific direction along a principal plane of thediffusive reflecting layer and the normal to the principal plane byincident light in a direction parallel to the normal, the first range ofviewing angles having the direction of the incident light as a referenceangle; a second range of viewing angles within which reflected lightrays of luminous flux of the predetermined proportion of the secondtotal luminous flux of reflection are obtained is defined, the secondtotal luminous flux being obtained by the incident light in the otherplane including an imaginary axis of the other direction along theprincipal plane of the diffusive reflecting layer and the normal to theprincipal plane, the second range of viewing angles having the directionof the incident light as a reference angle; and the first range isnarrower than the second range,—an initial average orientation imaginaryplane of the liquid crystal layer, including a typical director ofliquid crystal molecules in a dark or bright state and the normal to theprincipal plane of the diffusive reflecting layer, is substantiallyparallel to the specific plane.

This gives substantially constant retardation independent of viewingangles to the reflected light in the direction along the specific plane,which behaves like direct reflection, and thereby it is possible toreduce dependence of contrast on the viewing angle in the directionalong the specific plane. Therefore, it is possible to provide thebrightest possible image display with high visibility even in thedirection along the specific plane.

For this aspect, there may be provided an orientation film fordetermining such an initial molecular orientation of the liquid crystallayer that the initial average orientation imaginary plane is set to besubstantially parallel to the specific plane.

In this aspect, the specific direction and the other direction may havea substantially perpendicular relations. This allows the liquid crystaldisplay device having diffused reflected light distribution with adirectivity in directions perpendicular to each other to be furtherimproved in respect of a quality of displaying. Setting the specificdirection in particular to the vertical direction of the display face ofthe liquid crystal display device and setting the other direction to thehorizontal direction of the display face is suitable for the liquidcrystal display device used in portable devices. Since a display face ofthis type of display device is overwhelmingly more often viewed bychanging the viewing angle horizontally than it is viewed by changingthe viewing angle vertically, the ability to maintain a bright imagewhen the viewing angle is changed horizontally is very effective and atthe same time assures stability of contrast also when the viewing angleis changed vertically.

In the liquid crystal display device, the diffusive reflecting layer mayhave a reflecting surface showing roughness of shape based on aplurality of island-shaped outline units of depression or projectionportions, and an average diameter of the units of depression orprojection portions in the specific direction may be greater than anaverage diameter in a direction substantially perpendicular to thespecific direction on the principal plane of the diffusive reflectinglayer, and alternatively, an average pitch of the units of depressionportions or the units of projection portions in the specific directionmay be greater than an average pitch of them in a directionsubstantially perpendicular to the specific direction on the principalplane of the diffusive reflecting layer. This has advantages that adesired directivity can be added to the diffused reflected lightdistribution of the diffusive reflecting layer relatively simply and insophistication.

The liquid crystal display device according to the above-mentioned formscan be manufactured using a method of manufacturing a liquid crystaldisplay device comprising a liquid crystal layer for performing opticalmodulation in accordance with an image to be displayed and a diffusivereflecting layer for diffusively, reflecting light having passed throughthe liquid crystal layer to the liquid crystal layer with a diffusedreflected light distribution having a predetermined directivity,comprising the steps of forming the diffusive reflecting layer in such aform that the diffusive reflecting layer has a function of giving thereflected light a diffused reflected light distribution in which: afirst range of viewing angles within which reflected light rays ofluminous flux of predetermined proportion of the total luminous flux ofreflection are obtained is defined, the total luminous flux beingobtained in a specific plane including an imaginary axis of a specificdirection along a principal plane of the diffusive reflecting layer andthe normal to the principal plane by incident light in a directionparallel to the normal, the first range of viewing angles having thedirection of the incident light as a reference angle; a second range ofviewing angles within which reflected light rays of luminous flux of thepredetermined proportion of the total luminous flux of reflection areobtained is defined, the total luminous flux being obtained by theincident light in the other plane including an imaginary axis of theother direction along the principal plane of the diffusive reflectinglayer and the normal to the principal plane, the second range of viewingangles having the direction of the incident light as a reference angle;and the first range is narrower than the second range, forming anorientation film for determining an initial molecular orientation of theliquid crystal layer, in such a manner that an initial averageorientation imaginary plane of the liquid crystal layer, including atypical director of liquid crystal molecules in a dark or bright stateand the normal to the principal plane of the diffusive reflecting layer,is substantially parallel to the specific plane.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view schematically showing a structure of adiffusive reflecting layer forming member in the respective steps of amanufacturing method for a diffusive reflecting layer applied to thepresent invention.

FIG. 2 is a plan view schematically showing an example of photomask usedin the manufacturing method of FIG. 1.

FIG. 3 is a plan view schematically showing another example of photomaskused in the manufacturing method of FIG. 1.

FIG. 4 is an enlarged perspective view schematically showing outlines ofthe respective parts of a reflecting film of a diffusive reflectinglayer of FIG. 1 and a reflecting film of a comparison example thereto.

FIG. 5 is a graph showing a diffused reflected light distribution of adiffusive reflecting layer of FIG. 1.

FIG. 6 is a schematic view of a measuring form for obtaining the graphof FIG. 5.

FIG. 7 is a graph showing a characteristic of view angles versusreflectance for explaining a range of viewing angles in one specificplane of the diffusive reflecting layer of FIG. 1.

FIG. 8 is a graph showing a characteristic of view angles versusreflectance for explaining a range of viewing angles in another specificplane of the diffusive reflecting layer of FIG. 1.

FIG. 9 is a sectional view showing a general structure of a liquidcrystal display device of an embodiment according to the presentinvention.

FIG. 10 is a schematic perspective view for describing a combinationalmanner of a liquid crystal layer and a diffusive reflecting layer in theliquid crystal display device of FIG. 9.

DESCRIPTION OF THE PREFERRED EMBODIMENTS)

With reference to the attached drawings, the above aspects and otheraspects of the present invention will be described based on embodimentsin more detail below.

First, the diffusive reflecting layer used in embodiments of the presentinvention will be explained.

FIG. 1 shows a sectional structure of a member forming the diffusivereflecting layer in the respective steps of a manufacturing method for adiffusive reflecting layer.

In a first step (A), a support member 11 made of glass, for example, isprepared and a photoresist material of e.g. negative type is applied tothe entire surface of this support member 11 to a thickness of 2 μm toform a resist film 12 a. Then, after conducting prebaking, the resistfilm 12 a is exposed to light using a photomask.

FIG. 2 is a plan view schematically showing an example of photomask usedfor such exposure.

This mask has a plurality of openings 21 a arranged away from oneanother and these openings 21 a have an elliptic shape with a major axisof 6 to 14 μm and a minor axis of 3 to 7 μm, for example. In thisembodiment, the sizes of the openings 21 a may be the same or differentfrom one another, but the openings 21 a have substantially the samemajor axis direction and the same minor axis direction.

An average length of the major axis (average diameter) is, for example,10 μm and an average length of the minor axis (average diameter) is, forexample, 5 μm. Furthermore, for the later-described reasons, theseopenings 21 a have a pitch in the major axis direction (x-direction inFIG. 2) longer than a pitch in the minor axis direction (y-direction inFIG. 2) That is, the openings 21 a are provided more densely in theminor axis direction.

Besides the above-mentioned described mask 21, for example as shown inFIG. 3, it is also possible to use a mask 22 having polygonal openings22 a whose average diameter in the x-direction is different from theaverage diameter in the y-direction. It is also possible to use a maskhaving a mixture of elliptic openings and polygonal openings. In short,the photomask in this embodiment has openings with the average diameterin the x-direction being greater than the average diameter in they-direction perpendicular to the x-direction and with a pitch in thex-direction being greater than a pitch in the y-direction.

Using the elliptic opening mask 21 has an advantage of being able tohave a relatively simple structure. On the other hand, using thepolygonal opening mask 22 is preferable in that it facilitates thecontrol over angles of inclination of the surface of the reflecting film(see (E) in FIG. 1) which will be described later and allows the densityof the polygonal openings to be greater than that of the ellipticopenings.

It is noted that the average diameter in the x-direction of openings is,for example, 1.5 to 2 times the average diameter in the y-direction andthe pitch in the x-direction of openings is, for example, 1.5 to 2 timesthe pitch in the y-direction. In this way, the ratio of averagediameters in the x-direction to the y-direction is preferably the sameas the ratio of pitches in the x-direction to the y-direction.

In the next step (B), development is performed. In this way, the resistfilm 12 a is selectively left in correspondence with the openings of themask (portions other than the residual portions are dissolved andremoved) to form a plurality of depression portions 12 b, whereby aprojections and depressions layer 12 made up of the residual resist film12 a and the plurality of depression portions 12 b is formed. Theprojection portions 12 a correspond to the openings of the mask asdescribed above, and therefore the average diameter of the portions 12 ain the x-direction (horizontal direction in FIG. 1) is greater than theaverage diameter of the same in the y-direction (direction perpendicularto the surface of the sheet in FIG. 1) and the pitch thereof in thex-direction is greater than the pitch thereof in the y-direction. (B) inFIG. 1 indicates a sectional view taken along a line IB-IB in FIG. 2.

Furthermore, in the next step (C), post-baking is conducted at atemperature of, for example, 200° C. or above. This smoothens edges ofthe top face of the resist film 12 a and opening ends of the depressionportions 12 b. This post-baking may cause the average diameters of theprojection portions 12 a in the above-described x-direction andy-direction (diameters on the interface with the support member 11) tochange slightly but they are considered substantially the same.

After such post-baking, the process moves on to a step (D) in which aphotoresist is applied to the entire surface of the support member 11 soas to cover the projections and depressions layer 12 with thephotoresist under an application condition, for example, of a thicknessof 1 μm to form a projections and depressions adjusting layer 13 havingroughness of shape according to the projections and depressions layer12. This projections and depressions adjusting layer 13 is intended tofinally adjust roughness of shape of the reflecting film 14 (see (E) inFIG. 1) which will be described later. More specifically, theprojections and depressions adjusting layer 13 is formed in such a waythat the maximum angles of inclination of the surface of the reflectingfilm 14 has a desired value and the angles of inclination of the surfaceof the reflecting film in the area corresponding to the depressionportions 12 b of the projections and depressions layer 12 is alsochanged to desired angles to make the reflecting film 14 undulate as awhole.

Then, in a step (E), a metallic material such as aluminum or silver issputtered onto the entire surface of the projections and depressionsadjusting layer 13 to form the reflecting film 14 having a thickness of100 nm or more with projections and depressions (or with a roughenedsurface) by the projections and depressions layer 12 (and projectionsand depressions adjusting layer 13). This results in formation of acomposite layer 70 (referred to as “diffusive reflecting layer” in thepresent specification and it is a generic name also for other examplesof diffusive reflecting layers) provided with the projections anddepressions layer 12, projections and depressions adjusting layer 13 andreflecting film 14 on one side of the support member 11. The reflectingfilm 14 extends along the undulations formed of the projections anddepressions layer 12 and projections and depressions adjusting layer 13,and therefore the undulations of the surface of the reflecting film(reflecting surface) are also sparse in the x-direction and dense in they-direction.

FIG. 4 shows an example (a) of the projection portion of the reflectingfilm 14 and a comparative example (b) thereof.

In the example (a), a projection portion 14 a having an island-shapedoutline of the surface of the reflecting film 14 extends relatively longin the x-direction and the pitch of the projection portion in thex-direction is greater than the pitch in the y-direction. Thus, as awhole, a slope 14 _(x-z) which is inclined with respect to the x-z planehas a greater area than a slope 14 _(y-z) which is inclined with respectto the y-z plane. Here, z denotes a front-view direction of the entirereflecting film 14, in other words, the lamination direction of thereflecting film 14. “Pitch” here refers to the distance between thecenters of adjacent projections.

In this way, light incident on the reflecting film 14 is reflected moredominantly in the direction along the y-z plane as shown with dottedarrows in (a) of FIG. 4 and is likely to be reflected at various anglesas a whole. On the contrary, light reflected in the direction along thex-z plane is relatively scarce. Therefore, the light is reflected at awider range of angles in the direction along the y-z plane, while it isreflected at a narrower range of angles in the direction along the x-zplane, resulting in a diffused reflected light distribution having adirectivity.

On the other hand, in the example (b), the projection portion of thereflecting film 114 is symmetric with respect to the center (circularwhen viewed in the z-direction in this figure) and when the pitches ofthe projection portions in the x-direction and y-direction are the same,light is diffusively reflected uniformly in all directions as a whole.

Thus, the reflecting film 14 according to this embodiment having theprojection portions in the figure (a) whose pitches differ in thex-direction and y-direction can provide the reflected light with adirectivity as a whole.

FIG. 5 is a graph showing such a directivity and shows an example of thecase where light rays having certain constant intensity is incident ontothe reflecting film 14 from the front side.

A curve R_(x-z) denotes a reflectance with respect to the viewing angleson the x-z plane, while a curve R_(y-z) denotes a reflectance withrespect to the viewing angles on the y-z plane. The viewing angle 0°denotes a front view angle, that is, an angle when the reflecting film14 is viewed from the front side.

It is appreciated from these curves that reflected light of considerablystrong intensity is obtained only in a certain range of viewing anglesnear 0° on the x-z plane, while the intensity of the reflected lightdrops drastically when the reflected light goes away from that range. Inthe case of the y-z plane, it is appreciated that reflected light ofconsiderably strong intensity is obtained not only in the vicinity of 0°but also in a remarkably wide range of viewing angles centered at 0° isobtained and its viewing angle characteristic is quite different fromthat of the x-z plane.

More specifically, the graph having the diffused reflected lightdistribution as shown in FIG. 5 is obtained, as shown in FIG. 6, byplacing a light source 400 right above the diffusive reflecting layer70, making a ray of light incident onto the reflecting film 14 in thez-direction which is parallel to the normal to the principal plane ofthe diffusive reflecting layer and measuring the intensity of thereflected light within the plane of incidence of the incident light bymeans of optical detector 200 while changing a value of an angle θformed by the reflected light and the normal of incidence within theplane of incidence. Basically, the ratio of the intensity of thereflected light to the intensity of the incident light used here can beregarded as the reflectance of the vertical axis shown in FIG. 5 and theangle θ can be regarded as the viewing angle of the horizontal axis.FIG. 6 shows a mode of measuring the viewing angle characteristic in thedirection parallel to the x-z plane, but the same measuring way is alsoapplicable to the direction parallel to the y-z plane.

Here, when the reflectance obtained is expressed by R(θ) that is afunction of θ,

$\begin{matrix}{\lbrack {{Numerical}\mspace{14mu} {Formula}\mspace{14mu} 1} \rbrack \mspace{484mu}} & \; \\{\int_{- 90^{\circ}}^{+ 90^{\circ}}{{R(\theta)}{\theta}}} & (1)\end{matrix}$

is an expression from which the total sum of the reflectance within theplane of incidence is derived. The value of such a total sum can beregarded as equivalent to the total luminous flux of reflection withinthe plane of incidence, provided that the incident light is constant.

From FIG. 5 it is appreciated that the fact that the reflectance is highin the vicinity of viewing angle 0° is commonly applicable to both thecurve R_(x-z) and curve R_(y-z), but the actual curves may be morecomplicated curves or slightly asymmetric curves, and to deal with suchcases, it is desirable to define a range of viewing angles thatsatisfies certain conditions using the following equation.

$\begin{matrix}{\lbrack {{Numerical}\mspace{14mu} {Formula}\mspace{14mu} 2} \rbrack \mspace{490mu}} & \; \\{{\int_{- \varphi}^{+ \varphi}{{R(\theta)}{\theta}}} = {K{\int_{- 90^{\circ}}^{+ 90^{\circ}}{{R(\theta)}{{\theta ( {0 < K < 1} )}}}}}} & (2)\end{matrix}$

Here, the right side is the product of Formula (1) multiplied by apredetermined coefficient K, which is equivalent to a valuecorresponding to a certain proportion (K) of the total sum of thereflectance within the plane of incidence, and if the incident light isconstant, it is considered equivalent to luminous flux of thatproportion of the total luminous flux of reflection within the plane ofincidence. The left side is the total sum of the reflectance within theplane of incidence when the value of θ is changed from −φ to +φ forsatisfying a value according to the proportion of this right side. Theright side is a constant and the left side is a function whose variableis φ. Thus, the value of φ is obtained and this value indicates therange of viewing angles from which the luminous flux corresponding tothe proportion of the total luminous flux of reflection within the planeof incidence is obtained.

More practicably,

$\begin{matrix}{\lbrack {{Numerical}\mspace{14mu} {Formula}\mspace{14mu} 3} \rbrack \mspace{490mu}} & \; \\{{\int_{- \varphi}^{+ \varphi}{{R(\theta)}{\theta}}} = {0.5{\int_{- 80^{\circ}}^{+ 80^{\circ}}{{R(\theta)}{\theta}}}}} & (3)\end{matrix}$

is used.

The reason that the range of θ in the right side is set to −80° to +80°is that this range is a range in which a detector 200 is believed to beable to easily measure the intensity of reflected light and themeasurement will become actually difficult beyond this range.

As in Formula (3), it is possible to use 0.5 as the value of proportionK in practice. This indicates half areas of the total areas (areas withsingle hatching and cross hatching) of the domains enclosed by the curveR_(x-z) and curve R_(y-z) and the horizontal axis as shown in FIGS. 7and 8. In this example, the center (reference angle or front view angle)of the range of viewing angles which defines the half area is set to thedirection of the incident light (0°). Therefore, the half areas occupythe areas with cross hatching in FIGS. 7 and 8, respectively.

In this way, it can also be recognized from the graphs that the range ofviewing angles in which half of the total luminous flux of reflectionwithin the plane of incidence is obtained in the case (θ_(x-z)) of adirection parallel to the x-z plane is narrower than that in the case(θ_(y-z)) of a direction parallel to the y-z plane. If the value of K issmaller than 0.5, the cross-hatching area shown in FIGS. 7 and 8 becomessmaller, whereas if bigger, it is larger.

FIG. 9 shows a general sectional structure of a reflective liquidcrystal display device constructed using the diffusive reflecting layer70 having such characteristics.

The liquid crystal display device 100 in this example adopts an activematrix system using thin-film transistors (TFTs) as pixel drivingelements, but the present invention is not necessarily limited to this.

The liquid crystal display device 100 comprises, as members thatsandwich the liquid crystal medium, a front substrate 31 disposed on theside of incidence of external light and a rear substrate 41 disposedfacing the front substrate 31 with a predetermined gap in between. Thegap between the front substrate 31 and the rear substrate 41 is filledwith a liquid crystal layer 51 using a sealing member (not shown). Theliquid crystal layer 51 serves as an electro-optic medium for performingoptical modulation in accordance with the image to be displayed.

The front substrate 31 is a transparent substrate made of for example,glass and is provided on its inner side with a color filter 3C, a commonelectrode 32 consisting of a transparent conductor such as ITO (indiumtin oxide) and an orientation film 33 which defines initial orientationon the top side of the liquid crystal layer 51, in this order.

The rear substrate 41 is provided on inner side with a TFT-compositelayer 40 in which pixel driving TFTs are formed, the above-describeddiffusive reflecting layer 70 and an orientation film 49 which definesinitial orientation on the bottom side of the liquid crystal layer 51,in this order.

In the TFT-composite layer 40, a source electrode 42 a and a drainelectrode 42 b are formed away from each other and a semiconductor layer43 is formed between the source electrode 42 a and drain electrode 42 bfor coupling one with another at their respective ends. On thesemiconductor layer 43, a gate electrode 45 is formed through a gateinsulating film 44 having an opening for connection of the drainelectrode. The TFT having such a structure is formed for each of allpixels.

On the TFT-composite layer 40, the above-described diffusive reflectinglayer 70 is formed. More specifically, the projections and depressionslayer 12 having the above-described resist film 12 a and depressionportion 12 b is provided over the gate insulating film 44, gateelectrode 45 and drain electrode 42 b, and on this projections anddepressions layer, the above-described projections and depressionsadjusting layer 13 having an opening for connection of pixel electrodesis provided. On the projections and depressions adjusting layer 13 andits opening, the above-described reflecting film 14 is formed. Thisreflecting film 14 also functions as a so-called pixel electrode and isformed of a material having not only a light reflecting property butalso conductivity. Furthermore, the reflecting film 14 is connected tothe drain electrode 42 b through the openings provided in theprojections and depressions adjusting layer 13 and the gate insulatingfilm 44 and extends over the most area of each given pixel. On thereflecting film 14, an orientation film 49 is formed over the entirearea of the principal plane of the substrate.

The basic operation of the liquid crystal display device in such aconfiguration is described in the above-mentioned Patent Document 1 ormore, and so explanations thereof will be omitted here.

Next, combination architecture of the liquid crystal layer 51 and thediffusive reflecting layer 70, which is one of the important features ofthe present invention will be described.

FIG. 10 is a schematic view in which the liquid crystal layer 51 and thediffusive reflecting layer 70 are made a model, wherein one liquidcrystal molecule 5M which exists above the diffusive reflecting layer 70is representatively shown as a micro model of the liquid crystal layer51.

As is apparent from FIGS. 5 to 8, the diffusive reflecting layer 70 hasthe following requirements for a diffused reflected light distribution:

(1) a range of viewing angles θ_(x-z) within which reflected light raysof luminous flux of predetermined proportion (K) of the total luminousflux of reflection are obtained is defined, the total luminous flux ofreflection being obtained in a specific plane (x-z plane) including animaginary axis of a specific direction (x) along a principal plane (x-yplane) of the diffusive reflecting layer 70 and the normal (z-direction)to the principal plane by incident light in a direction parallel to thenormal, the range of viewing angles θ_(x-z) having the direction (0°) ofthe incident light as a reference angle; and

(2) a range of viewing angles θ_(y-z) within which reflected light raysof luminous flux of the predetermined proportion (K) of the totalluminous flux of reflection are obtained is defined, the total luminousflux being obtained by the incident light in the other plane (animaginary plane deviated substantially from the x-z plane, e.g. the y-zplane) including an imaginary axis of the other direction (directionsaway from the x-direction, for example, y-direction) along the principalplane of the diffusive reflecting layer 70 and the normal (z-direction)to the principal plane, the range of viewing angles θ_(y-z) having thedirection (0°) of the incident light as a reference angle.

In addition to them,

(3) is characterized in that the above-mentioned range of viewing anglesθ_(x-z) is narrower than the range of viewing angles θ_(y-z).

Furthermore, in such a case, the present invention specifies the optimumconditions for the liquid crystal layer 51 which is advantageous forimproving a quality of displaying.

According to such a specification, a plane (initial average orientationimaginary plane) a including a typical director 5 d of liquid crystalmolecules 5M in a dark or bright state of the liquid crystal layer andthe normal (imaginary line in the z-direction) to the principal plane ofthe diffusive reflecting layer 70 is oriented substantially in adirection of the specific plane (x-z plane) of the above-describeddiffusive reflecting layer, that is, substantially parallel to thespecific plane.

More specifically, the direction of the initial average orientationimaginary plane a is aligned with the direction of the specific plane ofthe diffusive reflecting layer based on the orientation direction of theorientation films 33 and 49 which contact to the liquid crystal layer 51at the top and bottom. For example, if the liquid crystal layer 51 is ofa homogeneous orientation type, it is only required to designate therubbing direction of the upper and lower orientation films 33 and 49 asthe x-direction. When the liquid crystal layer 51 is of a twistedorientation type, the rubbing direction of the upper and lowerorientation films 33 and 49 is determined in such a manner that theplane including the director of liquid crystal molecules of the centerportion of the liquid crystal layer 51 and the normal to the principalplane of the diffusive reflecting layer 70 is parallel to the specificplane (x-z plane), where the director of liquid crystal molecules of thecenter portion of the liquid crystal layer 51 is regarded as “averagedirector”.

Even if the liquid crystal layer 51 is of any orientation type otherthan these types, the “average director” of the liquid crystal moleculesmay be specified or estimated when the liquid crystal layer is in a darkor bright state to make a setting so that the initial averageorientation imaginary plane of the resultant director is substantiallyparallel to the specific plane of the diffusive reflecting layer.

It goes without saying that it is also possible to use other methods fordefining an initial orientation such as an oblique evaporation methodand optical orientation method instead of the rubbing treatment.

The characteristic of the diffusive reflecting layer 70 providing anarrow range of viewing angles within which reflection of at least thepredetermined intensity of the reflected light is caused on the x-zplane means that incident light in the x-z plane or a plane closethereto is easily made to be directly reflected and easily reflected inthe x-z plane likewise. This can be intuitively understood from aphenomenon that light incident on the liquid crystal layer 51 in asubstantially frontal direction of the screen is generally reflectedwith a directionality close to the frontal direction. Therefore, asshown in FIG. 7, light L1 incident in the x-z plane passes through theliquid crystal layer 51 at any angle and reaches the surface of thediffusive reflecting layer 70, while it is considered to be reflected asreflected light L1′ within the same plane, pass through the liquidcrystal layer 51 again and be directed to the front of the displaydevice 100.

According to the present invention, the following effects can beexpected by placing the x-z plane of the diffusive reflecting layer 70from which such behavior of light can be expected parallel to thespecific plane a of the liquid crystal layer 51.

That is, the total sum ret1 of a retardation Δnd1 and a retardationΔnd1' has a certain value, where the incident light L1 having a certainangle of incidence undergoes the retardation Δnd1 from the liquidcrystal layer 51 (liquid crystal molecule 5M) until it reaches thediffusive reflecting layer 70 and the reflected light L1′ therefromundergoes the retardation Δnd1’ from the liquid crystal layer 51, in theplane of incidence parallel to the x-z plane. Furthermore, the total sumret2 of a retardation Δnd2 and a retardation Δnd2′ also has a certainvalue, where the incident light L2 having a different angle of incidencewithin the same plane of incidence undergoes the retardation Δnd2 fromthe liquid crystal layer 51 (liquid crystal molecule 5M) until itreaches the diffusive reflecting layer 70 and the reflected light L2′therefrom undergoes the retardation Δnd2′ from the liquid crystal layer51 in the same plane of incidence, resulting generally in ret1=ret2 isheld. This is attributable to a phenomenon in which the total sum ofbirefringence of the liquid crystal molecules 5M that affects theincident light and birefringence that affects the reflected light doesnot change as long as the light follows the optical path of directreflection even if the liquid crystal molecule 5M is inclined as shownin the figure and even if the light has any angle of incidence. Thisphenomenon is called “retardation self-compensation effect”.

Therefore, the reflected light within this x-z plane is subjected t tosubstantially the same retardation even if the viewing angle changeswithin the x-z plane, and so the dependence of contrast on the viewingangle within the plane is preferably low.

On the other hand, the incident light at any angle within the y-z planeenters in a direction perpendicular to the average director, but it isdiffusively reflected at the diffusive reflecting layer 70, and theoptical path thereof is indeterminate. However, in this case,retardation of the liquid crystal changes asymmetrically with respectto, e.g. the front view direction and a variation of retardation withrespect to the variation of the viewing angle is small. As a result, thedependence of contrast on the viewing angle within the y-z plane as awhole remains stable as before.

Unlike the above description, if the x-z plane of the diffusivereflecting layer 70 and the specific plane at of the liquid crystallayer 51 are different in direction, the above-describedself-compensation effect cannot be expected. That is, the total sum ofretardation influencing the reflected light in the x-z plane whichbehaves like direct reflection varies depending on the angle ofreflection and the contrast changes according to the viewing anglewithin the plane. If the mismatch of direction is considerably large,there is a possibility that the whole area of the display face may turnblack even with a tiny variation of the viewing angle, that is, theso-called black crush may occur.

It may be preferable that the x-direction and y-direction in theabove-described embodiment are set to the vertical direction andhorizontal direction of a display face of the liquid crystal displaydevice respectively when the display face is viewed from the front. Thisis because reflective type liquid crystal display devices used inportable information terminal etc. is seldom in a mode of the displayscreen being viewed from the front by changing its angle vertically,while it is often in a mode of the screen being viewed by changing itsangle horizontally. This leads to effective use of light at viewingangles in the horizontal direction and the above-describedself-compensation effect also makes it possible to keep the contrastsatisfactorily even at the vertical viewing angle, to therebyconsiderably improve the quality of displaying in practical use.However, it goes without saying that the x-direction and y-direction mayalso be set as appropriate for other applications and purposes.

In order to implement the present invention effectively, it is desirableto make a large difference to some extent between the above-describedrange of viewing angles θ_(x-z) and the above-described range of viewingangles θ_(y-z). Furthermore, basically the above-described proportion Kpreferably has such a value that minimizes the range of viewing anglesthat satisfies the above-described certain requirements on the specificplane (x-z plane) with less diffusiveness is set as small as possible,but reducing K excessively will cause mirror reflection in the specificplane direction, and so it is preferable to select a compromise betweenthem.

The present invention has been explained so far, but the presentinvention is not limited to the above-described embodiments and can bemodified in various ways.

For example, the x-direction and y-direction are perpendicular to eachother, but they need not always be perpendicular to each other.

Furthermore, the present invention has been described with reference toa diffusive reflecting layer in which both the range of viewing anglesand the range of viewing angles θ_(y-z) are specified to a desiredspecification, but the present invention is applicable to any caseswhere only a range of viewing angles having the aforementionedrequirements within the specific plane including the imaginary axis inthe specific direction along the principal plane of the diffusivereflecting layer and the normal to the principal plane is defined to adesired specification and this range of viewing angles can be recognizedto be narrower than a range of viewing angles within the other planeincluding the imaginary axis in the other direction along the principalplane of the diffusive reflecting layer and the normal to the principalplane.

Furthermore, the above-described embodiment has taken specific examplesof the configuration of the diffusive reflecting layer and itsmanufacturing method, but the present invention is not limited to theseexamples. However, these examples are preferable in the sense that it ispossible to form the diffusive reflecting layer having a diffusedreflected light distribution with a desired directivity simply and insophistication

In addition, the above-described embodiment has been described about theactive matrix type reflective liquid crystal display device, but thepresent invention is also applicable to a transflective or passive type.Furthermore, the above example shows a so-called top-gate type TFT, butit goes without saying that a bottom-gate type TFT described in theabove-mentioned Patent Document 1 is also acceptable.

EXPLANATION OF SYMBOLS

-   11 . . . support member-   12 a . . . resist film-   12 b . . . depression portion-   12 . . . projections and depressions layer-   13 . . . projections and depressions adjusting layer-   14 . . . reflecting film-   70 . . . diffusive reflecting layer-   21, 22 mask-   21 a, 22 a . . . opening-   31 . . . front substrate-   3C . . . color filter-   32 . . . common electrode-   orientation film-   41 . . . rear substrate-   42 a . . . source electrode-   42 b . . . drain electrode-   43 . . . semiconductor layer-   44 . . . gate insulating film-   45 . . . gate electrode-   40 . . . TFT-composite layer-   51 . . . liquid crystal layer

1. A liquid crystal display device comprising a liquid crystal layer forperforming optical modulation in accordance with an image to bedisplayed and a diffusive reflecting layer for diffusively reflectinglight having passed through the liquid crystal layer to the liquidcrystal layer with a diffused reflected light distribution having apredetermined directivity, wherein the diffusive reflecting layer has afunction of giving the reflected light a diffused reflected lightdistribution in which: a first range of viewing angles within whichreflected light rays of luminous flux of predetermined proportion of thefirst total luminous flux of reflection are obtained is defined, thefirst total luminous flux being obtained in a specific plane includingan imaginary axis of a specific direction along a principal plane of thediffusive reflecting layer and the normal to the principal plane byincident light in a direction parallel to the normal, the first range ofviewing angles having the direction of the incident light as a referenceangle; a second range of viewing angles within which reflected lightrays of luminous flux of the predetermined proportion of the secondtotal luminous flux of reflection are obtained is defined, the secondtotal luminous flux being obtained by the incident light in the otherplane including an imaginary axis of the other direction along theprincipal plane of the diffusive reflecting layer and the normal to theprincipal plane, the second range of viewing angles having the directionof the incident light as a reference angle; and the first range isnarrower than the second range, an initial average orientation imaginaryplane of the liquid crystal layer, including a typical director ofliquid crystal molecules in a dark or bright state and the normal to theprincipal plane of the diffusive reflecting layer; is substantiallyparallel to the specific plane.
 2. A liquid crystal display device asdefined in claim 1, characterized by an orientation film for determiningsuch an initial molecular orientation of the liquid crystal layer thatthe initial average orientation imaginary plane is set to besubstantially parallel to the specific plane.
 3. A liquid crystaldisplay device as defined in claim 1 or 2, characterized in that thespecific direction and the other direction have substantially aperpendicular relations.
 4. A liquid crystal display device as definedin claim 1 or 2, characterized in that the specific direction is avertical direction of a display face of the liquid crystal displaydevice, and the other direction is a horizontal direction of the displayface.
 5. A liquid crystal display device as defined in any one of claims1-4, characterized in that the diffusive reflecting layer has areflecting surface showing roughness of shape based on a plurality ofisland-shaped outline units of depression or projection portions, and anaverage diameter of the units of depression or projection portions inthe specific direction is greater than an average diameter in adirection substantially perpendicular to the specific direction on theprincipal plane of the diffusive reflecting layer.
 6. A liquid crystaldisplay device as defined in claim 5, characterized in that an averagepitch of the units of depression portions or the units of projectionportions in the specific direction is greater than an average pitch ofthem in a direction substantially perpendicular to the specificdirection on the principal plane of the diffusive reflecting layer.
 7. Amethod of manufacturing a liquid crystal display device comprising aliquid crystal layer for performing optical modulation in accordancewith an image to be displayed and a diffusive reflecting layer fordiffusively reflecting light having passed through the liquid crystallayer to the liquid crystal layer with a diffused reflected lightdistribution having a predetermined directivity, comprising the stepsof: forming the diffusive reflecting layer in such a form that thediffusive reflecting layer has a function of giving the reflected lighta diffused reflected light distribution in which: a first range ofviewing angles within which reflected light rays of luminous flux ofpredetermined proportion of the total luminous flux of reflection areobtained is defined, the total luminous flux being obtained in aspecific plane including an imaginary axis of a specific direction alonga principal plane of the diffusive reflecting layer and the normal tothe principal plane by incident light in a direction parallel to thenormal, the first range of viewing angles having the direction of theincident light as a reference angle; a second range of viewing angleswithin which reflected light rays of luminous flux of the predeterminedproportion of the total luminous flux of reflection are obtained isdefined, the total luminous flux being obtained by the incident light inthe other plane including an imaginary axis of the other direction alongthe principal plane of the diffusive reflecting layer and the normal tothe principal plane, the second range of viewing angles having thedirection of the incident light as a reference angle; and the firstrange is narrower than the second range, forming an orientation film fordetermining an initial molecular orientation of the liquid crystallayer, in such a manner that an initial average orientation imaginaryplane of the liquid crystal layer, including a typical director ofliquid crystal molecules in a dark or bright state and the normal to theprincipal plane of the diffusive reflecting layer, is substantiallyparallel to the specific plane.